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20 April 2005 Use of energy imparted as an optimization tool in CT
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We have developed a patient dosimetry tool that will permit the optimization of image quality in CT. Published Monte Carlo CT dosimetry data were used to generate values of the energy imparted to an anthropomorphic phantom undergoing head and body CT examinations. Energy imparted factors E 5,n were computed for irradiation of 5 mm thick slabs of the anthropomorphic phantom, which were normalized to the free-in-air dose to muscle at the CT isocenter obtained in the absence of any phantom or patient. Calculations of E 5,n were obtained for CT scanners from five vendors and for 208 contiguous slabs of the anthropomorphic phantom ranging from the top of the head to the upper leg region. Values of E 5,n were relatively constant in the abdomen and chest region, but there was a large inter-scanner variability, with a mean of 170 ± 50 mJ/Gy for five vendors when E 5,n values were averaged over the whole trunk. The mean E 5,n for the neck region was 100 ± 20 mJ/Gy, which increased to 110 ± 30 mJ/Gy for the head region. Adding 0.25 mm Cu filtration increased the value of the normalized energy imparted value E 5,n by an average of 24%. Relative to 100 kVp, increasing the x-ray tube voltage by 20 and 30 kVp increased the normalized energy imparted value E 5,n by 10% and 14%, respectively. Patient energy imparted is useful for studying optimization strategies with respect to x-ray technique factors.
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Ari I. Jonisch, Walter Huda, and Kent M. Ogden "Use of energy imparted as an optimization tool in CT", Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005);

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